The semiconductor industry is continuously moving toward the fabrication of smaller and more complex integrated circuits with higher performance. One type of integrated circuit is an optical circuit that uses light or other electromagnetic radiation for circuit operations. Some common components of optical integrated circuits include light sources, detectors, and waveguides, where waveguides can provide many functions including transmitting, splitting, coupling, combining, multiplexing, demultiplexing, and switching optical signals. Planar lightwave circuits (PLC) are optical circuits that are produced on a plan, and are typically produced on a wafer. PLC technology can be used for many types of optical devices, including monolithic (optical functions only) and hybrid opto-electrical integrated circuits. Comparable optical fiber devices having similar functions to PLC devices would typically be much larger in size.
A planar waveguide transmits light, and some planar waveguides include a dual core structure. A first core is primarily used for transmitting light, and an adjacent second core reflects light into the first core. The dual core structure can increase the intensity of the light transmitted, because the second core can accept and direct more light into the first core than a similar sized first core without an adjacent second core. The second core typically has a refractive index that is slightly lower than the refractive index of the first core so the light is directed from the second core into the first core. The lower refractive index of the second core also serves to reflect light such that light within the first core tends to stay within the first core.
The alignment of the first and second cores should be very accurate. Transmitted light signals have ripples that degrade performance when the first and second cores are not properly aligned. However, alignment marks used to align the first and second cores, or to align other components of the PLC, are typically positioned under several layers with similar refractive indexes, such as the layers used to produce the first and second cores. A large distance between the surface of the uppermost layer of the plurality of layers and an alignment mark decreases the image of the alignment mark and thereby decreases the accuracy of the alignment. For example, the image of the alignment mark may be blurred or obscured. Furthermore, a plurality of layers with refractive indexes that are slightly different tend to shift the perceived location of the alignment mark and make accurate imaging of the alignment mark even more difficult.
Accordingly, it is desirable to provide integrated circuits with accurately aligned components for use in PLC devices, and methods for producing the same. In addition, it is desirable to provide integrated circuits with alignment marks that can be viewed more clearly than traditional alignment marks, and methods of producing the same. Furthermore, other desirable features and characteristics of the present embodiment will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention.